Pivotal knife-edge electrical contact and a method of manufacture thereof



April 1959 B. A. WHEELER 6 PIVOTAL KNIFEEDGE ELECTRICAL CONTACT AND AMETHOD OF MANUFACTURE THEREOF Filed May 29, 1957 Ava m4 4&[4/7.

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United States Patent Ofitice PIVOTAL KNIFE-EDGE ELECTRICAL CONTACT AND AMETHOD OF MANUFACTURE "THEREOF Bryce A. Wheeler, Los Angeles, Calif.,assignor to Hughes Aircraft Company, Culver City, Calif., a corporationof Delaware Application May 29, 1957, Serial No. 662,538 6 Claims. (Cl.339-8) This invention relates to electrical contact devices andparticularly to pivotal electrical contact devices and their method ofmanufacture.

Rotary electrical contact devices comprised of slip rings and brushesare well known to the art. Where constant electrical contact is desiredunder conditions of severe vibration, an increase in the brush pressurewill usually provide against arcing caused by the brush being jarredfrom the slip ring contact surface. If arcing does occur, there isirregular current flow and pitting of the slip ring contact surface.

Although an increase in brush pressure isoften a satisfactory method forpreventing arcing, this technique cannot satisfactorily be employed insituations involving low torque slip ring shaft rotations. An increasein brush pressure with such devices causes higher friction torques whichmay seriously interfere with shaft rotations. This problem isparticularly acute with gyro take-offs, for example, in which onlyfractional rotations may be involved but in which the introduction ofany material frictional effect operates adversely on the gyro device.

It is therefore an object of the present invention to provide animproved electrical contact device utilizing high brush pressure buthaving minimum friction torque.

It is another object of this invention to provide an improved electricalcontact device, operable with fractional rotations, which ischaracterized by low friction but high contact pressures.

It is another object of the a method for manufacturing for fractionalrotations and tion conditions.

In accordance with the present invention, these objects may be achievedby providing an electrical contact device having brushes in engagementwith a plurality of contact elements disposed along the pivotal axis ofa nonconductive base member. The base may enclose a portion of thecontact elements and plurality of conductors, each attached to a contactelement. The contact elements themselves have a contact surface which ismachined to a virtual knife-edge. The knife-edges of the contactelements permit the brushes to be adjusted so as to assert a highpressure on the contact surfaces but with minimum friction torque,because of the small area of contact, acting in reaction to the pivotingof the base member. As the base member is pivoted by a low torquesource, therefore, the brushes remain in contact even under vibrationconditions.

In accordance with another feature of this invention, a process isprovided for forming the virtual knife-edged contact surfaces and thebase member. The base member containing the contact elements may berotated about its pivotal axis while the machining apparatus, placedcoincident with the pivotal axis of the base member, machines thecontact surfaces to surfaces of extremely small radius. The radius ofthe contact surfaces may be made to approach zero by this method therebypermitting the contact element surfaces to acccommodate presentinvention to provide an electrical contact device for use under severevibra- 2,383,536 Patented Apr. 21, 1959 extremely high brushespressures. The resultant pivotal electrical contact device will providecontinuous electrical contact under severe vibration conditions whichcause arcing and will be particularly useful with slip ring shaftrotations of low torque.

The novel features which are believed to be characteristic of theinvention, both as to its organization and method of operation, togetherwith further objects and advantages thereof, will be better understoodfrom the following description considered in connection with theaccompanying drawing, in which like reference numerals refer to likeparts and in which:

Figs. 1 through 4 illustrate the steps of a process, in accordance withthe invention, by which a pivotal electric contact structure may beprovided. Fig. 1 is an isometric view of a first step in accordance withthe invention, showing a plurality of conductors attached to a pluralityof interconnected contact elements;

Fig. 2 is an isometric view, partly cut away, of structure provided in alater step in accordance with the invention, showing the contactelements and conductors of Fig. 1 positioned in a mold;

Fig. 3 is an isometric view a still later step in accordance with theinvention, illustrating the manner in which a nonconductive material ismolded about the conductors and a portion of the interconnected contactelements of Fig. 2;

Fig. 4 is an isometric view of a final step in accordance with theinvention, illustrating a method for machining the excess material fromthe interconnected contact elements molded in a nonconductive materialas in Fig. 3;

Fig. 5 is an isometric view of a pivotal electric contact structure inaccordance with the invention as employed as a gyro pick-off; and

Fig. 6 is a cross-sectional view of the pivotal electric contactstructure of Fig. 5, taken along the plane 6-6 of Fig. 5, showing afinished contact surface.

One application of the pivotal electric contact, as shown in Fig. 5, isto provide electrical take-offs for gyros which may operate with lowtorque shaft rotations. However, to better understand the invention andthe way by which high brush contact pressures are utilized to overcomethe arcing problem, a method by which the invention may be manufacturedis described first.

Referring now to Fig. l, a multiple fingered interconnected contactstrip 10, to be used to form the contact elements, is comprised of abase portion 11 and a plurality of fingered contact elements 12extending from the base portion 11. The contact elements 12 are made ofa conductive material such as silver, brass, or copper, all of whichhave both good conductive properties and good wearing qualities. Baseportion 11, which is later removed to separate the contact elements,provides a convenient means for handling the contact elements during thevarious manufacturing steps. Near the tips of each contact element issecured a conductor 13 which will provide a means for transmittingcurrent flow to the contact elements. The conductors are secured to thecontact elements as by soldering, welding, or brazing.

To form a body to align and support the contact elements l2 and toprotect the conductors 13, a nonconductive material such as a resinousplastic or ceramic is disposed about the conductors 13 and portions ofthe contact elements 32. Fig. 2 shows the contact strip 10 placed in amold 16 with the contact elements 12 and conductors 13 positioned in adie cavity 17 The contact strip is retained and positioned in the moldby a peg 14 inserted through an indexing hole 15 in the contact strip.The free ends of the conductors 13 are inserted into a shaft 18,

of structure provided in which also extends into the die cavity 17. The.

shaft 18 will form a part of the finished pivotal electrical contact aswill become more apparent.

After the contact strip 10 and shaft 18 are properly retained in themold 16, a nonconductive material is introduced into the die cavity 17and the hollow of shaft 18 to form a base member 19, shown in Fig. 3.The base member 19 is comprised of grooves 22, lands 21, and a shoulder20, which is joined to the shaft 18. The lands 21 serve to center thebrushes while the grooves 22 provide unobstructed access for the brushesto the contact element surfaces, and also protect conductor 13, shown inFig. 6, against damage during the subsequent machining step. Since thecontact elements 12 are now embedded in and supported by base member 19,the contact strip 10 including portion 11 is removed as by sawing,cutting, or machining along the dotted line 39 shown in Fig. 3.

To form the virtual knife-edged contact surface on the contact element,the shaft 18 is now supported in a collet 24, as shown in Fig. 4. A gangof circular saws 25, having individual saws 26 spaced on a shaft 27corresponding with the spacing of contact elements 12, is positionedsubstantially coincident with the pivotal axis line 23 of the basemember 19 and in contact with the exposed surfaces of contact elements12. By rotating collet 24, the base member structure 19 is moved throughan angle about the axis line 23, thereby permitting the saws 25 tomachine a small arcuate surface on the exposed portions of element 12.As an alternative method, the machining apparatus may be moved about thepivotal axis of the base member 19 while retaining the base member 19 ina fixed position. As shown in Fig. 6, the size of the angle throughwhich the base member 19 is moved about its pivotal axis 23 depends uponthe apex angle 28 formed by the surfaces of the grooves 22. With an apexangle of 120 degrees, the base member 19 would be required to be movedthrough an angle of 60 degrees about its pivotal axis. The radius of thearcuate contact surface 29 machined on the contact element 12 may bemade to approach zero. Radii of .001 of an inch have been machined whichpermit brush pressures up to approximately 40 times greater than thoseused in other electrical contact devices without any appreciableincrease in friction torque.

Fig. shows the finished electrical contact installed for use as a gyrotake-off assembly. The assembly is comprised of three brushes 32extending into a brush shaft 31. Encased within shaft 31 are threeconductors 33, each of which is secured to a brush and serves totransmit the electrical current picked up from the contact surfaces 12by the brushes. The brush shaft 31 containing conductors 33 is insertedthrough a frame block 35 into a frame member 39 which provides supportfor the brush shaft. A bolt 34 is used to engage the shaft and to biasthe brushes 32 into engagement with the arcuate contact surfaces ofcontact elements 12.

The shaft 18 of the base member 19 is inserted through a caging arm 36and is rotatably mounted in the bearing 37 in the frame member 30. Theextension of shaft 18 is interconnected with a gyro shaft (not shown).As base member 19 pivots about its axis 23 in response to gyro shaftmovements, therefore, the electrical current, carried by the conductorsencased in the base member 19, is transmitted to the contact element 12where it is picked up by the brushes 32. For severe vibrationconditions, the brushes may be adjusted to exert considerable pressureon the contact element so as to resist being jarred from the contactsurfaces.

It is seen that there has been disclosed a pivotal electrical contactdevice for use in connection with contact brushes, and its method ofmanufacture. The device and method disclosed provide a plurality ofelectrical contact elements having contact surfaces of extremely smallradius which will accommodate high contact brush pressures. Because thecontact surfaces are a virtual knifeedge, the high brush pressures causeno appreciable increase in friction torques to interfere with thepivoting action of a low shaft torque contact device. The high brushpressures are utilized to maintain constant electrical contact duringoperation under severe vibration condition and eliminate arcing causedby the brushes being jarred from the contact surface.

- What is claimed is:

1. A pivotal electrical contact structure adapted for use in connectionwith contact brushes comprised of:

-a conductor, a contact element secured to said conductor,

a nonconductive pivotal base member disposed about said conductor and aportion of said contact element, said contact element having an arcuatecontact surface and having a point thereon coincident with a pivotalaxis of said base member, whereby a point contact is maintained betweensaid contact elements and the brushes.

2. A pivotal electrical contact structure adapted for use in connectionwith contact brushes, said structure comprising: a conductor, a contactelement secured to said conductor, a nonconductive pivotal base memberdisposed about portions of said conductor and said contact element, saidbase member having substantially the configuration of a sector of aright cylinder with an apex angle of less than 180 degrees, said contactelement having an arcuate contact surface and having a point thereoncoincident with a pivotal axis of said base member, whereby a pointcontact is maintained between said contact element and the brushes.

3. A pivotal electrical contact structure adapted for use in connectionwith contact brushes, said structure comprised of: three conductors,three contact elements, each secured to a different one of saidconductors, an elongated nonconductive base member having alternategrooves and lands spaced substantially equal along the longitudinallength thereof and perpendicular to a pivotal axis of said base member,said base member having substantially the configuration of a sector of aright cylinder with an apex angle at said pivotal axis of less thandegrees and said base member being disposed about said conductors andportions of said contact elements, said contact elements being equallyspaced along the length of said base member in said grooves of said basemember and having an exposed brush contact surface at said pivotal axisof said base member, said brush contact surface having an arcuateconfiguration and having a point thereon at a distance less than .003 ofan inch from said pivotal axis of said base member, whereby a virtualknifeedge contact is maintained between said contact elements and thebrushes during pivoting of said pivotal electrical contact structureabout said pivotal axis and through said apex angle of said base member.

4. A pivotal electrical contact assembly comprising: a first conductor,a contact element secured to said first conductor, a nonconductive basemember pivotable about a longitudinal axis and disposed about said firstconductor and a portion of said contact element, said contact elementhaving an arcuate contact surface and having a point thereon coincidentwith the pivotal axis of said base member, a brush positionedsubstantially perpendicular to the longitudinal axis of said base memberand in operative relation to the arcuate surface of said contactelement, whereby continuous electrical contact is maintained betweensaid brush and said arcuate contact surface during pivoting of said basemember about its pivotal axis.

5. A pivotal electrical contact assembly comprising: a nonconductiveshaft, three filamentous brushes attached perpendicular to and along thelongitudinal length thereof, a first group of three conductors securedto said brushes and encased in said shaft, a second group of threeconductors, three contact elements secured to said second group ofconductors, an elongated nonconductive base member having alternategrooves and lands spaced substantially equal along the longitudinallength thereof and perpendicular to a pivotal axis of said base member,

said base member having substantially the configuration of a sector of aright cylinder With an apex angle at said pivotal axis of less than 120degrees, said grooves of said exposed brush contact surface adapted toengage said brushes at said pivotal axis of said base member, said brushcontact surface having an arcuate configuration and having a pointthereon at a distance less than .003 of an inch from said pivotal axisof said base member, whereby a virtual knife-edge contact is maintainedbetween said contact elements and said brushes during pivoting of saidbase member about its pivotal axis and through said apex angle of saidbase member.

6. A pivotal electrical contact essembly comprising: a

an elongated nonconductive base memgrooves forming an apex angle at saidpivotal axis of less that 180 degrees, a plurality of contact elementsindividually disposed along said pivotal axis of said base conductorsembedded in said shaft, of filamentous brushes, each secured to adifferent one of said conductors,

biased into engagement with the of said contact References Cited in thefile of this patent UNITED STATES PATENTS Klym Sept. 15, 1953 MereteyMar. 26, 1957

